The overall objective of the research is to elucidate the nature of conditioned inhibition (CI), established with aversive stimuli, by isolating those factors and operations which control its development and maintenance. The specific aims of the research are: (1) to extend and conclude earlier comparisons of the different conditioning procedures that purportedly produce CI (e.g., "explicitly unpaired," backward, trace, delay, "Pavlovian," and differential); (2) to evaluate different general theories of the phenomenon, as well as specific hypotheses regarding factors which affect its development (e.g., contingency, "negative discrepancy," contextual conditioning, relaxation, and rehearsal); (3) to assess the relationship of CI to both conditioned and unconditioned opponent (or analgesic) reactions, as well as determine whether aversively based CI either modulates or is itself influenced by the production of endogenous opiates; relatedly, (4) to evaluate CI's role as a modulator of (or an "antagonist" to) excitatory-response thresholds via either its direct action or possible regulation of opponent and analgesic reactions: (5) to extend investigation of CI's functional dependency on a memorial representation of the excitatory stimulus used to produce it, primarily by assessing the role of excitation (cf. fear) in maintaining CI established in excitatory extinction and higher-order conditioning; and finally, (6) to evaluate the specificity of the findings by examining the effects of selected procedures on CI development with an appetitive (e.g., food) conditioned or unconditioned stimulus. Most of the research will employ a conditioned-suppression methodology involving licking for water (or bar-pressing for food) as the baseline response. But where appropriate, a "hot-plate" procedure will be used to assess changes in pain sensitivity produced by conditioned analgesic reactions, and in other extensions, a response-latency technique will be employed to assess appetitive conditioning. The significance of the research is viewed not only in terms of enhanced knowledge of conditioning processes and related mental-health practices concerning the regulation of fear, but also in terms of the potential deployment of CI as a behavioral analogue to addiction processes.